Three-phase a



March 24, 1964 c, CLASQN ETAL 3,126,465

THREE-PHASE A.C. ELECTRIC CIRCUIT-BREAKER Filed June 23, 1960 2Sheets-Sheet 1 INVENTORS 2 2 "4, z mlwzlc Pb/457;.

ATTORNEYS March 24, 1964 J. c. CLASON ETAL 5 THREE-PHASE A.C. ELECTRICCIRCUIT-BREAKER Filed June'23, 1960 2 Sheets-Sheet 2 INVENTO S UnitedStates Patent 3,126,465 THREE-PHASE A.. ELECTRIQ CIRCUIT-BREAKER Jan C.Clason and Geert C. Damstra, Heugelo, Netherlands, assignors to N.V.Fabriek Van Eiectrische Apparaten Voorheen F. Hazemeijer & (30.,Hengelo, Netherlands, a corporation of the Netherlands Filed June 23,1960, er. No. 38,158 Claims priority, application Netherlands June 30,1959 Claims. (Cl. 200-445) The invention relates to a three-phase A.C.power circuit-breaker, in which in three parallel planes lie threecurrent loops with substantially parallel legs and each of these loopsis provided with one or two arc-control devices-each incorporated in oneof the parallel legswith lateral gas outlets, each of said arc-controldevices containing a stationary contact and cooperating with alongitudinally movable switching member. Various constructions of suchcircuit-breakers are known. A construction with two arc-control devicesfor each loop is described in Schakelingen, No. 33, March 1942, p. 474.The so-called Conel circuit-breaker, illustrated in Schakelingen, No.58, July 1956, p. 23, forms a construction with one arc-control devicefor each loop.

The invention has arisen from experiments with circuitbreakers of thetype mentioned, with two arc-control devices for each current loop, fromwhich it appeared that upon interruption of the current noproper arcpositioning is attained, i.e., that when an arc is drawn in thearc-control devices and when gas under pressure consequently develops insaid arc-control devices, the arc is unsteady and does not take up theproper position in front of the gas outlet. This phenomenon limits thecircuit-breaking capacity of the circuit-breaker.

The invention meets this difiiculty to a considerable degree andmoreover opens various favourable new possibilities.

Itis characterized in that in the central loop the gas outlet of eacharc-control device lies in the plane through the two legs of this loop;that in each of the two outer loops the gas outlet of each arc-controldevice diverges relative to the gas outlet of the correspondingarc-control device of the central loop to a value a, determined by theformula (2) Ct C20 b in which a has a value of about 25 n is about 2.8,a is the distance between the two legs of each of the loops, and b isthe distance between the planes of adjacent loops; and that the ratioa/b is between about 0.75 and about 0.45.

As will be elucidated below, a striking improvement of the arepositioning is achieved with this construction, to the extent thatduring a first experiment with an arrangement with two'arc-controldevices for each current loop an approximate doubling of thecircuit-breaking capacity was already possible.

With regard to a three-phase circuit-breaker of the type mentioned inthe first paragraph of this specification it is known that the resultantof the forces which are exerted on any given leg, i.e. also on an aredrawn in that leg, by the currents in all the other'legs, as a functionof time may assume values greatly varying in direction and magnitude.Owing to this the arc positioning is greatly hampered (Schakelingen, No.58, p. 19).

FIGURE 1 is a view in section of 6 conductors which define the currentloops of the three phases.

FIGURES 2 through 4 show one embodiment of the invention. FIGURE 2 is avertical section, FIGURE 3 is a horizontal section along the lineIII-III of FIGURE Patented Mar. 24, 1964 2 and FIGURE 4 is adiagrammatic plan on a smaller scale of the six arc-control devices.

The invention is based, among other things, on the realization that theratio of the distance a between the two legs of each of the loops to thedistance b between the planes of adjacent loops, i.e. the ratio a/ b, isa quantity which in several respects is decisive for the properties ofthe circuit-breaker. This may be elucidated with reference to FIGURE 1,in which a diagrammatic crosssection is given of the six conductorswhich form the legs of the current loops of the three phases. On each ofthe legs forces are exerted by the currents in the other legs. It hasbeen found that the greatest forces occur during the switching of highlyasymmetric currents such as may occur for low values of cos (p, a powerfactor. It has also been found that under these most unfavourablecircumstances the main direction of the 'electrodynamic forces acting oneach of the arcs, for the central loop lies in the plane through the twolegs of this loop, while that for the two outer loops is determined bythe formula in which a is the angle indicated in FIGURE 1 between thesaid main direction and the plane of the loop in question, 00 is afactor of about 25, and n is an exponent with a value of about 2.8. Bythe main direction is to be understood the direction in which thegreatest electrodynamic force occurs. Now according to the invention, inorder that the arc positioning may become as favourable as possible forall the phases, these realizations are taken into account in positioningthe gas outlets in the arc-control devices of the different phases inthe way formulated above by making the centre lines of the various gasoutlets to coincide everywhere with the said main direction.

This is done, also according to the invention, over a range of the ratioa/ b extending from about 0.75 to about 0.45. The reason of this willappear later.

It has also been found that with the two outer loops it is possible topoint out for each leg an angular range in which 5 has a value of about40, while a, b and n have the same meaning as mentioned above.

It is seen that Formula II is of the same kind as Formula I. This meansthat as the ratio a/ b is reduced to distinctly below the value 1, notonly the angle a but also the range ,8 of the direction of the resultantbecomes more than proportionately smaller, a fact which is actuallybound to promote an optimum arc positioning under any circumstances.

Further it has been found that with the central loop it is possibletopoint out for each leg an angular range 'y, likewise locatedsymmetrically relative to the main direction, within which range theresultant of the forces may fluctuate, and that the magnitude of thisrange 7 is approximately twice that of the range ,8; in this case themain direction .of theelectrodynamic force lies in the plane through thetwo legs of the central loop. From this it follows that for this loop,too, the arc positioning is geratly improved by a reduction of the ratioa/ b.

The realization embodied in the Formula II for [3 makes it possible tochoose the actual angular width 6 of the gas outlets of the arc-controldevices, viewed from the centre line of the arc-control device inquestion, in

the right way. For the two outer phases this angular width 5 may bechosen at least equal to u, and for the central phase at least equal to'y. In this way it is ensured that during the switching the arc does notcome into contact with the edges of the gas outlet, or at least aslittle as possible, a feature which greatly prolongs the life of thearc-control devices. On the other hand the dimensions of the outlets arepartly also conditioned by the requirement of obtaining the gas pressureand velocity necessary for the arc extinction. From this point of view,too, a reduction of the ratio 11/17 is favourable. It results in a morethan proportionate reduction of the required minimum angular width ofthe gas outlet and thus provides for ample play for the adaptation ofthe gas outlet openings to the required gas pressure.

As stated above, the invention covers a range of the ratio a/b extendingfrom about 0.75 to about 0.45. In fact, if this ratio is distinctlygreater than 0.75, and if it is, for instance, nearly 1 or more than 1,which is the case with the above mentioned known circuit-breaker of theSchakelingen, No. 33, March 1942, publication with two arc-controldevices for each loop, then-as has now been foundthe value of ,8determined by Formula II (and thus certainly that of *y as well) isalready so great that it is no longer possible at all to develop in thearc-control devices a gas pressure and velocity suflicient for theextinction of the arc. 'In that case therefore it is senseless to followthe said formula.

If on the other hand the ratio a/ b were made distinctly smaller than0.45, a case would present itself which is already known for one controldevice for each current loop from the Conel circuit-breaker referred toabove in the Schakelingen, No. 58, July 1956, publication, and in whichthe angle determined by Formula I becomes so small (at most a fewdegrees) that it is not necessary at all to design the two outer currentloops differently from the central one as regards the direction of theirgas outlets.

By means of the invention, however, a striking increase of thecircuit-breaking capacity is achieved in the aforesaid range of a/bbetween about 0.75 and about 0.45, both when two arc-control devices foreach loop are used and when one arc-control device for each loop isused.

The section of FIGURE 2 lies in the plane of one of the three phases.The two other phases lie behind the plane of the drawing.

The current loops of three phases are arranged in parallel planes in avessel 1 filled with an insulating medium,

such as oil. Each loop comprises a contact bridge 2 with two parallelcontact rods 3, which cooperate with two stationary contacts 4. Each ofthese stationary contacts 4 is located in an arc-control device 5, made,e.g., of nylon, containing insulating bodies 15 and 16, with a lateralgas outlet 6. Both the stationary contact 4 and the arccontrol device 5are supported by a lead-in insulator 7 passing through the cover 8 ofthe vessel 1.

The contact bridges 2 of the three loops are coupled with and operatedby a joint member 9, which extends perpendicular to the plane of thedrawing in the vessel 1 and in a way not shown can be moved down with aview to opening the circuit-breaker and up with a view to closing thecircuit-breaker. FIGURE 2 shows the circuit-breaker at a moment it is incourse of being opened. Between each contact rod 3 and each stationarycontact 4 an arc 10 is then drawn. In the arc-control device 5 gas underhigh pressure develops in the known way, which gas escapes through thegas outlet 6.

The two arc-control devices 5 in FIGURE 2 are placed so close togetherthat they are in contact with each other, in order to obtain a smallratio a/b. In the diagrammatic plan of FIGURE 4 the distances a and bare given; their ratio is less than 0.75.

The two arc-control devices of the central loop have gas outlets whichare directed away from each other in the plane through the two legs ofthis loop. The two arc-control devices of each of the two outer loopshave gas outlets each of which diverges over the angle on relative tothe gas outlet of the corresponding arc-control device of the centralloop. As appears from FIGURE 3, the actual angular width 6 of the gasoutlets is at least p for the two outer phases and at least 7 for thecentral phase (which cannot be seen). In the case of a successfullyapplied value of the ratio a/b of about 0.6 the divergence a is aboutand the angle 5 is about 10.

The invention of course also applies to a double arccontrol device, inwhich the two individual devices are combined to one singleconstructional unit.

What we claims is:

1. A three-phase A.C. electric circuit-breaker in which in threeparallel planes lie three current loops with substantially parallel legsand each of these loops is provided with at least one arc-controldevice--each incorporated in one of the parallel legswith lateral gasoutlets, each of said arccontrol devices containing a stationary contactand cooperating with a longitudinally movable switching member,characterized in that in the central loop and gas outlet of eacharc-control device lies in the plane through the two legs of said loop;that in each of the two outer loops the gas outlet of each arccontroldevice diverges relative to the gas outlet of the correspondingarc-control device of the central loop to a value a, determined by theformula a D e in which 04 has a value of 25, n is 2.8, a is the distancebetween the two legs of each of the loops, and b is the distance betweenthe planes of adjacent loops; and that the ratio a/ b is in the rangebetween 0.75 and 0.45.

2. Apparatus according to claim 1, characterized in that each of the gasoutlets of the two outer loops, viewed from the centre line of thearc-control device in question, has an angular range of at least {3,determined by the formula in which d has a value of 40.

3. An apparatus according to claim 2, characterized in that each of thegas outlets of the central loop, viewed from the centre line of thearc-control device in question,

has an angular range of at least 7, approximately equal to ReferencesCited in the file of this patent Schakelingen, No. 58, July 1956, pp.17-23.

1. A THREE-PHASE A.C. ELECTRIC CIRCUIT-BREAKER IN WHICH IN THREEPARALLEL PLANES LIE THREE CURRENT LOOPS WITH SUBSTANTIALLY PARALLEL LEGSAND EACH OF THESE LOOPS IS PROVIDED WITH A LEAST ONE ARC-CONTROLDEVICE-EACH INCORPORATED IN ONE OF THE PARALLEL LEGS-WITH LATERAL GASOUTLETS, EACH OF SAID ARC-CONTROL DEVICES CONTAINING A STATIONARYCONTACT AND COOPERATING WITH A LONGITUDINALLY MOVABLE SWITCHING MEMBER,CHARACTERIZED IN THAT IN THE CENTRAL LOOP AND GAS OUTLET OF EACHARC-CONTROL DEVICE LIES IN THE PLANE THROUGH THE TWO LEGS OF SAID LOOP;THAT IN EACH OF THE TWO OUTER LOOPS THE GAS OUTLET OF EACH ARCCONTROLDEVICE DIVERGES RELATIVE TO THE GAS OUTLET OF THE CORRESPONDINGARC-CONTROL DEVICE OF THE CENTRAL LOOP TO A VALUE A, DETERMINED BY THEFORMULA